Method of improving pressure sensor measurement by passive current compensation

Abstract

A simplified method and apparatus for electronic pressure control with compensation for current operating temperature and pressures in which computer memory is employed for storing a plurality of firmware models which characterize the effects of temperature and pressure variations on (1) fluid flow through the flow restrictor, (2) the temperature sensor, and (3) the pressure sensor, so that control signals can be generated which compensate a plurality of thermally coupled sensors for changes in current operating temperatures and pressures.

What is claimed is: 
     
       1. A return current balancing circuit for use with a pressure sensor having a return current which varies with temperature, the return current causing voltage fluctuations in a conductor that couples the pressure sensor to ground, comprising: a first voltage supply terminal coupled to a first supply voltage (V+),   a return current terminal coupled by the conductor to ground and providing a return path for the return current,   a second voltage supply terminal coupled to a second supply voltage (V-), the second supply voltage having a lower potential than said ground, and   a variable resistive circuit connected between said return current terminal and said second voltage supply terminal, the resistive circuit having a resistance which varies with temperature, whereby a variable current flowing through the resistive circuit substantially reduces the return current.   
     
     
       2. The return current balancing circuit as claimed in claim 1, wherein the return balancing circuit couples the pressure sensor to a data acquisition system having a ground reference, and wherein, the variable resistive circuit substantially reduces the return current from the pressure sensor to the ground reference of the data acquisition system and substantially reduces the voltage drop associated with the intrinsic resistance of the conductor coupling the sensor's ground terminal to the data acquisition system ground reference. 
     
     
       3. The return current balancing circuit as recited in claim 2, said variable resistive circuit further comprising: a first fixed resistor R1 connected between said return current terminal and said second voltage supply terminal;   a second fixed resistor R2 connected at one end to said second voltage supply terminal; and   a temperature sensitive resistor Rt connected between the other end of the second fixed resistor R2 and said return current terminal.   
     
     
       4. The return current balancing circuit as recited in claim 3, whereby the variable resistive circuit is incorporated as part of the sensor. 
     
     
       5. The return current balancing circuit as recited in claim 3, whereby the variable resistive circuit is incorporated as part of a module supporting multiple sensors. 
     
     
       6. The return current balancing circuit as recited in claim 3, said variable resistive circuit further comprising: a temperature measurement terminal Vtemp connected to the junction of said fixed resistor R2 and said temperature sensitive resistor Rt, wherein the voltage output (Vtemp=Rt/(Rt+R2)*V-), measured between said temperature measurement terminal Vtemp and said return current terminal is proportional to temperature.